a. Field of the Invention
The invention generally relates to catheters for guided introduction into a body cavity. More specifically, the invention relates to a catheter that includes a distal deflectable segment having an anisotropic deflecting (or bending) stiffness that reduces or eliminates unintended out-of-plane movement of a distal end of the catheter.
b. Background Art
Catheters can be used for medical procedures to examine, diagnose, and treat while positioned at a specific location within the body that is otherwise inaccessible without more invasive procedures. During these procedures a catheter is typically inserted into a vessel near the surface of the body and is guided to a specific location within the body for examination, diagnosis, and treatment. For example, catheters can be used to convey an electrical stimulus to a selected location within the human body, e.g., for tissue ablation, as well as to monitor various forms of electrical activity in the human body, e.g., for electrical mapping. Catheters are also being used increasingly for medical procedures involving the human heart. In such cases, the catheter is typically inserted in an artery or vein in the leg, neck, or arm of the patient and guided, sometimes with the aid of a guide wire or introducer, through the vessels until a distal end of the catheter reaches a desired location in the heart.
In a normal heart, contraction and relaxation of the heart muscle (myocardium) takes place in an organized fashion as electro-chemical signals pass sequentially through the myocardium. Sometimes abnormal rhythms occur in the heart, which are referred to generally as cardiac arrhythmia. The cause of such arrhythmia is generally believed to be the existence of an anomalous conduction pathway or pathways that bypass the normal conduction system. An increasingly common medical procedure for the treatment of certain types of cardiac arrhythmia is catheter ablation. During conventional catheter ablation procedures, an energy source is placed in contact with cardiac tissue (e.g., associated with an anomalous conduction pathway) to create a permanent scar or lesion that is electrically inactive or noncontractile. The lesion partially or completely blocks the stray electrical signals to lessen or eliminate arrhythmia. As will be appreciated, ablation of a specific location within the heart requires the precise placement of the ablation catheter within the heart.
Guidance of a catheter to a specific location in the body can be performed using feel, electrophysiological guidance, computer generated maps/models and/or a combination of the above. In any case, it may be necessary to deflect the distal end of the catheter to facilitate movement of the catheter through a body cavity (e.g., vessel) and/or to position the distal end of the catheter relative to an internal structure of interest. In this regard, guidable catheters and/or introducers typically include a selectively deflectable segment near their distal tip. For instance, an ablation catheter may include a distal end portion (e.g., insertion portion) having an ablation electrode and a soft and flexible distal deflectable segment that is disposed between the electrode and the relatively rigid (e.g., metallic wire-braided) catheter shaft that extends to a proximal actuator. Pull wires extend through the deflectable segment and attach to a pull ring (e.g., positioned between the deflectable segment and the electrode). The pull wires extend through the catheter and are axially connected to a pull mechanism of the proximal actuator. Upon the deflection by manipulating the actuator, the pull wires generate a pull force that imposes a bending moment on the flexible deflectable segment. This leads to the deflection of the distal end of the catheter, which allows the distal end to be routed to and/or positioned relative to desired internal locations.
Several difficulties may be encountered, however, when attempting to precisely locate the distal end of a catheter at an internal location of interest for guidance purposes and/or for performing an internal procedure, such as, for example, ablating tissue.